Exercise of jaw muscles is an important part of treatment and rehabilitation for many jaw injuries and disorders. For example, the common practice of wiring jaws closed as a splinting approach to fractures and bone surgical procedures leads to a shortening of the muscles that close the jaw and a weakening of the muscles that open it. As a result, patients may find it impossible to open their mouths after the wiring has been removed. Physicians and surgeons resort to expedients which include prying with tongue depressors and the use of screw operated wedge devices to stretch the muscles and thereby accomplish opening of the mouth. Once the jaws are opened, it is necessary for patients to undertake exercises to stretch the muscles in order to regain full freedom of motion. Though to date jaw exercise devices have considered only opening and closing movement of the jaw, it may be desirable to impart lateral as well as pivotal movement to the mandible during its normal opening and closing movement as therapeutic movement of the temporo-mandibular joint as well as the muscle system for mandibular control. Passive elastic devices have been suggested for accomplishing jaw exercising. Also, expensive spring operated instruments have been developed for this purpose.
A typical defect of most commercially available jaw exercising devices is that they either cause pain and injury through exertion of excessive force or they may apply pressure to the molar region in a vertical manner thus displacing the condyles downward and disrupting the temporo-mandibular joint. None of these devices moves the lower jaw in a fashion which takes into account the structural features of the jaw hinge established by the temporo-mandibular joint, namely that the pivotal area of the jaw hinge is above and to the rear of the mouth opening by virtue of the curvature of the jaw at its upper rear portion and that the temporo-mandibular joint does not establish a single precise, pivot point about which the mandible rotates. Rather, the temporo-mandibular joint forms a movable pivot which causes compound movement of the mandible throughout its rotation.
During the healing period following maxillofacial surgery, as mentioned above, the mandible is typically immobilized by wires or other suitable retainers to stabilize the bone structure during its healing. After an appropriate period of healing has been accomplished the mandible is released from its stabilized relation with respect to the maxillary arch and a period of therapy begins. During therapy, as the jaw muscles return from their typically atrophied condition and as the temporomandibular joint recovers from its lack of vertical and lateral movement, it is desirable to measure the degree of jaw opening and lateral jaw movement that can occur as the patient's therapy progresses. It is desirable therefore to provide a measurement device having the capability of measuring vertical jaw movement from a particular reference and also having the capability of measuring lateral jaw movement in relation to a particular reference.
Because a jaw movement measuring device may come into contact with oral fluid it is particularly desirable to provide a measurement device that can be autoclaved or otherwise rendered sterile or which can be disposed of in order to prevent any cross contamination that might otherwise occur between patients or between the medical personnel and a patient. It is thus desirable to provide a jaw opening and lateral movement measuring device which is effective for selective measurement of both jaw movement and lateral jaw movement and which can also be sterilized or disposed of as desired by the user to prevent the possibility of bacterial or viral cross contamination.